User operation
17
MAXXfl o EVO Lite
3.8.1 Error codes (continued)
Error
Code
Error Code
Description
Diag.
Code
Notes
110
SLT Lockout
306 431
432 433
434 435
436 756
Electronic temperature limits exceeded. General overheating issue. Check for
pump operation, trapped air and heat exchanger blockages. Monitor tempera-
tures of system to establish problem area.
429 818
Safe reset of the error sub code 433 (see above) has not been met. Allow the
water heater to cool further before resetting.
305 412
550 551
754
Mechanical overheat protection circuit is open circuit (connection X18 on
control PCB). Check connector is fully inserted
426 437
815
Flow temperature heat up gradient exceeded. Check pump operation and
presence of trapped air in the heat exchanger. Flow through heat exchanger
may be restricted.
438
817
Maximum Delta T of system exceeded. Check pump operation and presence
of trapped air in the heat exchanger. Flow through heat exchanger may be
restricted.
428
Maximum Delta T of system exceeded. Initial starting of the pump before the
burner is operated, can cause this error. If accompanied by code 429 within
the same minute, this error can be disregarded.
429
Safe reset of the error sub code 428 /438 (see above). Allow the water heater
to cool further before resetting.
427 816
Safe reset criteria has not been met. Allow the water heater to cool further
before resetting.
420 421
819 820
Return temperature greater than fl ow temperature. Check that the fl ow and
return sensors are operating correctly
419 430
813 814
Flow temperature limit exceeded. Check for overheating issues and fl ow sen-
sor (B2) performance.
809 810
422 423
Flow temperature not plausible - Reading less than 0
O
C or greater than
124
O
C . Check fl ow sensor (B2) and replace if necessary.
425
812
Return temperature limit exceeded. Check for overheating issues and return
sensor (B7) performance.
424
811
Return temperature not plausible - Reading less than 0
O
C or greater than
124
O
C . Check return sensor (B7) and replace if necessary.
111
Shutdown limit
thermostat
264
Heat exchanger temperatures have been exceeded. Investigate fl ow rates
and controls to determine causes of temporary fault code.
125
Maximum boiler
temperature
exceeded
286 500
740
Temperature supervision lockout. Check pump, shutoff valves, burner and
fl ow rates before resetting
501
Temperature has not increased at fl ow sensor after burner start. Check fl ow
sensor is correctly clipped to pipe work.
502
Temperature has not increased at return sensor after burner start. Check
return sensor is correctly clipped to pipe work.
126
DHW charging
temperature not
reached
72
Charging temperature not achieved within parameterised time scale. Check
operation and heat up times for heater
127
DHW legionella
temperature not
reached
73
Check operation of legionella function and DHW system. Legionella setpoint
has not been achieved within 48 hours of the legionella function operating.
When using a secondary return system and sensor, do not set the legionella
function setpoint too high, as the heat losses of the hot water pipework may
not permit this setpoint to be achieved at the return point before the heater.
